The present invention relates to tools, and, more specifically, to devices for cutting holes in wood and other construction materials.
Hole cutting devices for use in the construction trades typically consist of hole saws, auger bits, and spade-type bits. Several limitations are inherent in these traditional devices, such as cleanliness of cut, speed of cut, ability to cut large diameters with relatively low torque, and the ability to cut an interrupted or partial hole. Because of the proliferation of battery powered drilling devices, tools that cut large diameter holes without stalling or exceeding the torque capabilities of these devices have not been available. Also, as with rehabilitation construction, sometimes there are nails or screws hidden in the work piece that can fatally damage the saw or bit""s cutting edge.
Previous attempts at solving these problems have been only marginally successful. For example, a hole saw shown in U.S. Pat. No. 5,803,677 to Brutscher et al. (xe2x80x9cBrutscherxe2x80x9d) probably provides a fast cut, but the raker teeth provided on the hole saw add additional torque, and the hole saw, because of the number and placement of cutting teeth, does not offer an ideal load distribution and balance.
Further, in U.S. Pat. No. 5,597,274 to Behner (xe2x80x9cBehnerxe2x80x9d), a hole cutter has a single cutting bit for reducing torque. However, the single-bit design adds to undesirable wobble and instability, as well as to a slower cutting speed.
Accordingly, a primary object of the present invention is to provide a tubular hole cutter that has an optimized cutting load distribution, and that offers a fast, low torque, clean cut, even for large-diameter and interrupted or partial holes.
A tubular hole cutter comprises a tubular side wall and a circular backing plate attached to one end of the tubular side wall. The backing plate is configured for attachment to a conventional heavy-duty hole saw arbor. At an end opposite to the backing plate, the tubular side wall has a generally smooth, annular end surface interrupted by three gullets extending longitudinally in the side wall parallel to the axis of the hole cutter. The gullets are spaced equally about the circumference of the tubular side wall. Three cutting bits are attached to the tubular side wall at respective trailing edges of the gullets, i.e., spaced equally apart by 120xc2x0, with one cutting bit per gullet. This configuration allows the tubular hole cutter to place a maximum force, transferred to the object under the cutting edges, without binding the tool or resulting in an undesired angled offset hole. Additionally, the cutting bits are configured, according to a particular geometrical design, to produce a smooth, balanced, and precise cut, to reduce torque, and to reduce cutting bit wear, among other things.
In use, initially, the hole cutter is attached to a hole saw arbor, and the arbor is affixed to a drill or other power tool. The central pilot drill bit from the arbor engages the work piece to provide a stabilizing hole until the cutting bits engage the work piece. The outer edges of the cutting bits are configured to contact the work piece first, causing a scoring action that greatly reduces any rough surface at the entry and exit of the cut. This also creates a lip or flange on the exit side of the cutout, or xe2x80x9cpuck,xe2x80x9d that causes the puck to resist being drawn all the way into the hole cutter, thus allowing the puck to be more easily removed. During cutting the chips generated by the cutting bits are ejected into the gullets. Once the cutting operation is finished, the puck produced by the cut is then easily removed by hand or with a screwdriver or similar tool.
The multiple cutting bits share a reduced chip load resulting in lower cutting torque. The combination of multiple cutting bits, the shape of the bits, and the limitation of the depth-of-cut of the cutting bits by the annular end surface between the gullets provides a stable, low torque cut, even with larger diameters. This is especially desirable when using battery operated drilling devices.
When drilling an interrupted or partial (i.e., semi-circular) hole, the equally-spaced multiple bits facilitate continuous engagement with the work piece even when cutting with as little as about 52% of the surface diameter of the tubular hole cutter.